Navegando por Autor "Durin, Gianfranco"
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Artigo Quantitative Scaling of Magnetic Avalanches(American Physical Society, 2016-08-15) Durin, Gianfranco; Bohn, Felipe; Corrêa, Marcio Assolin; Sommer, Rubem Luis; Doussal, P. Le; Wiese, K. J.We provide the first quantitative comparison between Barkhausen noise experiments and recent predictions from the theory of avalanches for pinned interfaces, both in and beyond mean field. We study different classes of soft magnetic materials, including polycrystals and amorphous samples—which are characterized by long-range and short-range elasticity, respectively—both for thick and thin samples, i.e., with and without eddy currents. The temporal avalanche shape at fixed size as well as observables related to the joint distribution of sizes and durations are analyzed in detail. Both long-range and short-range samples with no eddy currents are fitted extremely well by the theoretical predictions. In particular, the short-range samples provide the first reliable test of the theory beyond mean field. The thick samples show systematic deviations from the scaling theory, providing unambiguous signatures for the presence of eddy currentsArtigo Universal properties of magnetization dynamics in polycrystalline ferromagnetic films(American Physical Society, 2013-09-23) Bohn, Felipe; Corrêa, Marcio Assolin; Viegas, Alexandre da Cas; Papanikolaou, Stefanos; Durin, Gianfranco; Sommer, Rubem LuisWe investigate the scaling behavior in the statistical properties of Barkhausen noise in ferromagnetic films. We apply the statistical treatment usually employed for bulk materials in experimental Barkhausen noise time series measured with the traditional inductive technique in polycrystalline ferromagnetic films having different thickness from 100 to 1000 nm and determine the scaling exponents. Based on this procedure, we group the samples in a single universality class, since the scaling behavior of Barkhausen avalanches is characterized by exponents τ ∼ 1.5, α ∼ 2.0, and 1/σ νz ∼ ϑ ∼ 2.0 for all the films. We interpret these results in terms of theoretical models and provide experimental evidence that a well-known mean-field model for the dynamics of a ferromagnetic domainwall in three-dimensional ferromagnets can be extended for films.We identify that the films present an universal three-dimensional magnetization dynamics, governed by long-range dipolar interactions, even at the smallest thicknesses, indicating that the two-dimensional magnetic behavior commonly verified for films cannot be generalized for all thickness rangesArtigo Universality beyond power laws and the average avalanche shape(Springer Nature, 2011-01-23) Papanikolaou, Stefanos; Bohn, Felipe; Sommer, Rubens Luis; Durin, Gianfranco; Zapperi, Stefano; Sethna, James P.The study of critical phenomena and universal power laws has been one of the central advances in statistical mechanics during the second half of the past century, explaining traditional thermodynamic critical points1, avalanche behaviour near depinning transitions2,3 and a wide variety of other phenomena4. Scaling, universality and the renormalization group claim to predict all behaviour at long length and timescales asymptotically close to critical points. In most cases, the comparison between theory and experiments has been limited to the evaluation of the critical exponents of the power-law distributions predicted at criticality. An excellent area for investigating scaling phenomena is provided by systems exhibiting crackling noise, such as the Barkhausen effect in ferromagnetic materials5. Here we go beyond powerlaw scaling and focus on the average functional form of the noise emitted by avalanches—the average temporal avalanche shape4. By analysing thin permalloy films and improving the data analysis methods, our experiments become quantitatively consistent with our calculation for the multivariable scaling function in the presence of a demagnetizing field and finite field-ramp rate